Fig. 4. Hypoxia influences the expression of genes associated with mesoderm differentiation. RT-PCR assays performed on RNA isolated from normoxic or hypoxic undifferentiated (ES) and EB cultures. (A) RT-PCR analyses of Arnt^+/+ cells and two independent Arnt^–/– lines differentiated under normoxic (N, 21%) or hypoxic (H, 3%) conditions. ß-actin serves as a loading control. (B) Relative levels of gene expression from Arnt^+/+ and Arnt^–/– cultures under normoxic (N, 21%) or hypoxic (H, 3%) conditions assayed by real-time detection (RTD)-PCR. Transcripts are normalized to 18S RNA.